X-band system performance of the very large array

The Very Large Array (VLA) is being equipped to receive telemetry from Voyager2 during the Neptune encounter in 1989. Cryogenically cooled amplifiers are being installed on each of the 27antennas. These amplifiers are currently a mix of fieM effect transistors (FETs) and high electron mobility transistors (HEMTs) and exhibit zenith system temperatures that range from 30 K to 52 K. We summarize the system temperatures and aperture efficiencies determined during the past year. The nominal values of the noise diode calibration are compared with derived values made under the assumption of a uniform atmosphere over the array. Gain values are determined from observations of unresolved radio sources whose flux densities are well known. The tests suggest that the completed VLA will have a ratio of gain to system temperature that is approximately 4.4 dB above that of a single 64-m antenna of the Deep Space Network.